Image sensor

ABSTRACT

A substrate includes a plurality of pixels arranged in a two-dimensional array structure and has a front side and a back side opposite to the front side. An interconnection is arranged on the front side of the substrate. An insulating layer, a color filter, and a micro-lens are arranged on the back side of the substrate. A pixel separation structure is disposed in the substrate. The pixel separation structure includes a conductive layer having a grid structure in a planar view of the image sensor and surrounds each of the plurality of pixels. A back side contact is vertically overlapped with and electrically connected to a grid point portion of the grid structure of the conductive layer of the pixel separation structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/862,396, filed on Jan. 4, 2018, which claims priority under 35 U.S.C.§ 119 to Korean Patent Application No. 10-2017-0040214, filed on Mar.29, 2017, in the Korean Intellectual Property Office, the disclosure ofeach of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The inventive concept relates to an image sensor.

DISCUSSION OF RELATED ART

Image sensors are semiconductor devices that convert an optical image toan electrical signal. Image sensors are generally classified intocharge-coupled device (CCD) image sensors and complementary metal oxidesemiconductor (CMOS) image sensors. As the semiconductor devices becomeincreasingly integrated, the image sensors are also becoming more highlyintegrated. As the size of each pixel is reduced, occurrence of a defectdue to a dark current or a charge accumulation in an interfaceincreases.

SUMMARY

According to an exemplary embodiment of the present inventive concept,an image sensor is provided as follows. A substrate includes a pluralityof pixels arranged in a two-dimensional array structure and has a frontside and a back side opposite to the front side. An interconnection isarranged on the front side of the substrate. An insulating layer, acolor filter, and a micro-lens are arranged on the back side of thesubstrate. A pixel separation structure is disposed in the substrate.The pixel separation structure includes a conductive layer having a gridstructure in a planar view of the image sensor and surrounds each of theplurality of pixels. A back side contact is vertically overlapped withand electrically connected to a grid point portion of the grid structureof the conductive layer of the pixel separation structure.

According to an exemplary embodiment of the present inventive concept,an image sensor is provided as follows. A plurality of pixels eachincludes a photodiode disposed in a substrate and has a front side and aback side, the plurality of pixels being arranged in a first directionand a second direction to form an array structure in a planar view ofthe image sensor. A pixel separation structure penetrates the substrate.The pixel separation structure includes a plurality of sidewallinsulating layers, and a conductive layer having a grid structuresurrounding each of the plurality of sidewall insulating layers. Aplurality of back side contacts each is partially inserted into one of aplurality of grid point portions of the grid structure of the conductivelayer. The plurality of grid point portions of the grid structure of theconductive layer is non-overlapped in the first direction and in thesecond direction with the plurality of pixels.

According to an exemplary embodiment of the present inventive concept,an image sensor having a voltage source generating a voltage is providedas follows. A plurality of photodiodes is disposed in the substrate andarranged in a first direction and in a second direction intersecting thefirst direction in a planar view of the image sensor. A pixel separationstructure penetrates the substrate, surrounds each of the plurality ofphotodiodes and separates the plurality of photodiodes from each other.An interconnection is electrically connected to the pixel separationstructure and applied with the voltage having a negative voltage or aground voltage. A plurality of back side contacts is arranged in a thirddirection intersecting the first direction and the second direction inthe planar view of the image sensor and electrically connected to theinterconnection through the pixel separation structure. The plurality ofback side contacts each is partially inserted in a region of the pixelseparation structure. The region of the pixel separation structure issurrounded by a predetermined number of the plurality of photodiodes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present inventive concept will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the accompanying drawings of which:

FIG. 1 is a plan view of a part of a pixel of an image sensor accordingto an exemplary embodiment of the present inventive concept;

FIG. 2 is a circuit diagram of a pixel included in the pixel of theimage sensor of FIG. 1 according to an exemplary embodiment of thepresent inventive concept;

FIG. 3 is a cross-sectional view taken along line I-I′ of FIG. 1according to an exemplary embodiment of the present inventive concept;

FIG. 4 is an enlarged view of a portion “A” of the image sensor of FIG.1, according to an exemplary embodiment of the present inventiveconcept;

FIGS. 5A through 5C are plan views of image sensors according to anexemplary embodiment according to an exemplary embodiment of the presentinventive concept;

FIGS. 6A through 6C are perspective views of 3D structures of a backside contact formed in the image sensor of FIG. 1 according to anexemplary embodiment of the present inventive concept;

FIG. 7 is a cross-sectional view of an image sensor according to anexemplary embodiment of the present inventive concept;

FIGS. 8A and 8B are cross-sectional views of image sensors according toan exemplary embodiment of the present inventive concept;

FIGS. 9A and 9E are cross-sectional views of image sensors according toan exemplary embodiment of the present inventive concept; and

FIG. 10 is a schematic block diagram of a camera system including animage sensor according to an exemplary embodiment of the presentinventive concept.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a plan view of a part of a pixel of an image sensor 100according to an exemplary embodiment and schematically shows only apixel Px, a pixel separation structure 110, and a back side contact 120for convenience of understanding. As used herein, singular “a,” “an,”and “the” are intended to cover the plural forms as well, unless thecontext clearly indicates otherwise. FIG. 2 is a circuit diagram of thepixel Px included in the image sensor 100 of FIG. 1. FIG. 3 is across-sectional view taken along line I-I′ of FIG. 1. FIG. 4 is anenlarged view of a portion “A” of the image sensor 100 of FIG. 1.

Referring to FIGS. 1 through 4, the image sensor 100 includes asubstrate 101, a photodiode PD, the pixel separation structure 110, theback side contact 120, a multi-layered interconnection 140, a colorfilter 162, and a micro-lens 164.

The substrate 101 may include a silicon bulk wafer or an epitaxialwafer. The epitaxial wafer may include a crystalline layer grown on abulk wafer by an epitaxial process. In this case, the substrate 101 maybe formed of an epitaxial layer. The substrate 101 is not limited to thebulk wafer or the epitaxial wafer. For example, the substrate 101 mayinclude various other types of wafers, such as a polished wafer, anannealed wafer, and a silicon-on-insulator (SOI) wafer.

The substrate 101 includes a front side FS and a back side BS. As shownin FIG. 3, the multi-layered interconnection 140 is arranged on thefront side FS, and the color filter 162 and the micro-lens 164 arearranged on the back side BS. Light may be incident on the back side BSthrough the micro-lens 164. In this case, the image sensor 100 is a backside illumination (BSI) image sensor in which the light is incident onthe back side BS of the substrate 101. If a combined structure of thephotodiode PD and an interlayer insulating layer 130 are upside-down andattached to the micro-lens 164, light is incident on the front side FSof the substrate 101. In this case, the image sensor 100 may be a frontside illumination (FSI) image sensor.

A pixel area or an active pixel sensor (APS) area including the pixel Pxmay be arranged in the substrate 101. The APS area may have arectangular shape when viewed as a horizontal cross-section, but a shapeof the APS area viewed as the horizontal cross section is not limited tothe rectangular shape. FIG. 1 is a plan view viewed from a back side ofthe substrate 101, showing a part of the APS area. For the convenienceof descriptions, an antireflection layer 151, the color filter 162, themicro-lens 164 as shown in FIG. 3 are omitted. A peripheral circuit areamay be arranged outside the APS area.

The pixel Px may absorb the incident light, generating and accumulatingelectric charges corresponding to the amount of the incident light. Thepixel Px includes the photodiode PD and a well area PW, which are formedin the substrate 101. The photodiode PD and the well area PW may beformed by performing an ion implantation process on the APS area withimpurities having opposite polarities. For example, in a case that thesubstrate 101 is includes a P-type epitaxial wafer, the photodiode PDmay be doped with N-type impurities, and the well area PW may be dopedwith P-type impurities. The photodiode PD may be relatively deeplyformed in the substrate 101 from the front side FS to the back side BS.The well area PW may be relatively shallowly formed in the substrate 101from the front side FS to the back side BS.

As shown in FIG. 2, the pixels Px includes the photodiode PD, a transfertransistor Tx, a source follower transistor Sx, a reset transistor Rx,and a selection transistor Ax. The transfer transistor Tx, the sourcefollower transistor Sx, the reset transistor Rx, and the selectiontransistor Ax may include a transfer gate TG, a source follower gate SF,a reset gate RG, and a selection gate SEL, respectively.

The photodiode PD may include an N-type impurity area and a P-typeimpurity area. A drain of the transfer transistor Tx corresponds to afloating diffusion area FD. In addition, the floating diffusion area FDis a source of the reset transistor Rx. The floating diffusion area FDis electrically connected to a source follower gate SF of the sourcefollower transistor Sx. The source follower transistor Sx is connectedto the selection transistor Ax. The reset transistor Rx, the sourcefollower transistor Sx, and the selection transistor Ax may be shared bypixels adjacent to each other, and thus a degree of integration may beincreased.

An operation of the image sensor 100 will be described with reference toFIG. 2. In a light-blocking state, a source voltage V_(DD) may beapplied to a drain of the reset transistor Rx and a drain of the sourcefollower transistor Sx to discharge electric charges remaining in thefloating diffusion area FD. Then, if the reset transistor RX is turnedoff and external light is incident on the photodiode PD, electron-holepairs may be generated in the photodiode PD. The holes move to theP-type impurity area, and the electrons move to the N-type impurityarea. If the transfer transistor Tx is turned on, the electric chargesare transferred to and accumulated in the floating diffusion area FD. Agate bias of the source follower transistor Sx may be changed inproportion to the accumulated amount of the electric charges, and avariation in source potential of the source follower transistor Sx mayoccur. In this regard, a signal caused by the electric charges may beread out through a column line CL by turning on the selection transistorAx.

The pixel separation structure 110 is arranged in the substrate 101 toseparate the pixel Px from each other. The pixel separation structure110 has a mesh structure or a grid structure on an x-y plane, as shownin FIG. 1. In addition, a height of the pixel separation structure 110correspond to a thickness of the substrate 101. As shown in FIG. 3, thepixel separation structure 110 connects the front side FS and the backside BS of the substrate 101. For example, the pixel separationstructure 110 penetrates the substrate 101 to extend from the front sideFS to the back side BS.

The pixel separation structure 110 includes a sidewall insulating layer111 and a conductive layer 113 arranged in the sidewall insulating layer111. The sidewall insulating layer 111 may be formed of an insulatingmaterial having a refractive index that is different from a refractiveindex of the substrate 101. For example, the sidewall insulating layer111 may include a silicon oxide layer, a silicon nitride layer, or asilicon oxynitride layer. The sidewall insulating layer 111 extends fromthe front side FS of the substrate 101 to the back side BS of thesubstrate 101.

The conductive layer 113 may be formed of polysilicon or polysilicondoped with impurities but the material of the conductive layer 113 isnot limited thereto. For example, the conductive layer 113 may be formedof any type of conductive material that may gap-fill a trench of thesidewall insulating layer 111. For example, the conductive layer 113 maybe formed of at least one of a metal, a metal silicide, and a conductivematerial containing a metal.

Meanwhile, since the pixel separation structure 110 has the meshstructure that is a single unitary structure, the conductive layer 113has the mesh structure as a single unitary structure. Accordingly, theconductive layer 113 is integrally connected structure and thus is anelectrically single body structure. In other words, if electric power isapplied to any portion of the conductive layer 113, the electric powermay be supplied entirely to the conductive layer 113.

Since the pixel separation structure 110 is formed over the front sideFS to the back side BS of the substrate 101, the pixel Px is separatedfrom each other, thereby preventing crosstalk caused by obliquelyincident light from occurring. The photodiode PD is in contact with andsurrounded by one of the sidewall insulating layer 111 in plural of thepixel separation structure 110. In this case, the photodiode PD may havethe same area as that of the pixel Px, and a light receiving area of thephotodiode PD increases, thereby increasing a fill factor, and thusquantum efficiency (QE) may be increased.

The well area PW is arranged above the photodiode PD in the front sideFS of the substrate 101. The transistors Tr described with reference toFIG. 2 may be arranged above the well area PW. For example, thetransistors Tr may be disposed closer to the front surface FS in thewell area PW. In FIG. 3, only a gate electrode 105 of the transistors isbriefly illustrated. Shallow trench isolation (STI) layers 103 a and 103b may be arranged in the well area PW to define an active area of eachof the transistors Tr. The STI layers 103 a and 103 b each has a depthshallower than the sidewall insulating layer 111. The STI layer 103 aand the sidewall insulating layer 111 may be integrally coupled to eachother in some areas. For example, the pixel separation structure 110 maybe coupled to the STI layer 103 a by penetrating through the STI layer103 a. In this case, the sidewall insulating layer Ill 1 is in contactwith the STI layer 103 a. Therefore, the STI layer 103 a and the pixelseparation structure 110 may have a “T” shape when viewed as a crosssection between two neighbouring pixels.

In FIG. 3, the back side contact 120 is formed on the back side BS ofthe substrate 101. The back side contact 120 is connected to theconductive layer 113 of the pixel separation structure 110 through theantireflection layer 151 disposed on the back side BS of the substrate101. A lower portion of the back side contact 120 is inserted into theconductive layer 113 but is not limited thereto. For example, the backside contact 120 has a lower surface that is in contact with an uppersurface of the conductive layer 113. For example, the back side contact120 may partially penetrate the antireflection layer 151. In this case,the back side contact 120 may be buried in the antireflection layer 151.An upper portion of the back side contact 120 protrudes from theconductive layer 113, and the upper portion of the back side contact 120is surrounded by the antireflection layer 151. The back side contact 120has an upper surface that is coplanar with an upper surface of theantireflection layer 151 at substantially the same height from the backside BS of the substrate 101.

The back side contact 120 may have a cylindrical shape. However, theshape of the back side contact 120 is not limited to a cylindricalshape. For example, the back side contact 120 may have variousthree-dimensional shapes, which will be described with reference toFIGS. 5A to 6. The back side contact 120 may be formed of tungsten (W).The material of the back side contact 120 is not limited to W. Forexample, the back side contact 120 may be formed of a metal materialsuch as Al, TiN, and an Al compound including Ti or Ta.

The back side contact 120 is disposed on the back side of the substrate101 and connected to the conductive layer 113 of the pixel separationstructure 110, thereby effectively preventing an electrostatic discharge(ESD) bruise effect of the image sensor 100 from occurring. The ESDbruise defect refers to a defect such as a blemish that occurs in animage because charges generated by ESD or the like accumulate on aninterface between the back side BS of the substrate 101 and theantireflection layer 151. The back side contact 120 connected to theconductive layer 113 of the pixel separation structure 110 is formed onthe back side BS of the substrate 101, and thus charges accumulated onthe interface between the back side BS and the antireflection layer 151may be discharged through the back side contact 120 and the conductivelayer 113. Specifically, the conductive layer 113 of the pixelseparation structure 110 may be electrically connected to aninterconnection layer 141 a disposed on the front surface FS of thesubstrate 101, and a ground voltage or a negative voltage may be appliedto the interconnection layer 141 a, and thus charges accumulated on theinterface may be discharged to the interconnection layer 141 a throughthe back side contact 120 and the conductive layer 113. For example, theconductive layer 113 of the pixel separation structure 110 iselectrically connected to the interconnection layer 141 a through avertical contact 142 a. As a result, the image sensor 100 of the presentembodiment may effectively remove the ESD bruise defect problem by usingthe back side contact 120 connected to the conductive layer 113.

As shown in FIG. 3, the image sensor 100 includes a voltage source 170generating a voltage including the negative voltage or the groundvoltage. For example, the voltage source 170 may be electricallyconnected to the interconnection layer 141 a so that the chargesaccumulated on the interface between the back side BS of the substrate101 and the antireflection layer 151 are removed by the voltage source170.

As shown in FIG. 1, the back side contact 120 is disposed in a gridpoint portion of the pixel separation structure 110 formed in atwo-dimensional grid structure on an x-y plane, for example, in a planarview of the image sensor 100. For example, the pixel Px is arranged in atwo-dimensional array structure in the planar view of the image sensor100, and the pixel Px has a rectangular structure on the x-y plane. Forexample, the pixel Px is arranged in a first direction (x-direction) andin a second direction (y-direction) to form the two-dimensional arraystructure. In this case, the back side contact 120 in plural is arrangedin a third direction (k-direction) intersecting the first direction andthe second direction. In an exemplary embodiment, the third direction isparallel to the line I-I′ of FIG. 1.

In addition, the pixel Px is separated from each other by the pixelseparation structure 110 of the two-dimensional grid structure. The backside contact 120 is disposed in a grid point portion of the pixelseparation structure 110 where vertexes of a predetermined number of thepixel Px may be adjacent to each other. For example, the predeterminednumber is four. In this case, four pixels surround the grid pointportion of the pixel separation structure 110. The four pixels, forexample, are arranged in two rows and two columns. Each row includes twopixels of the four pixels along the first direction. Each columnincludes two pixels of the four pixels along the second direction. Thegrid point portion of the pixel separation structure 110 isnon-overlapped in the first direction and in the second direction withthe four pixels.

Since the back side contact 120 is disposed in the grid point portion ofthe pixel separation structure 110, a process margin forming the backside contact 120 may be secured. For example, as shown in FIG. 4, theback side contact 120 having a first width W1 is disposed in the gridpoint portion of the pixel separation structure 110, and the back sidecontact 120 is apart from the sidewall insulating layer 111 adjacent tothe back side contact 120 by an interval of a second width W2. On theother hand, if the back side contact 120 is formed on a side portion ofthe pixel separation structure 110, i.e., a portion adjacent to a sideof the pixel Px, the back side contact 120 is apart from the sidewallinsulating layer 111 by an interval of a third width W3. However, thethird width W3 is smaller than the second width W2 so that a processmargin for forming the back side contact 120 is not sufficient.

The width W1 of the back side contact 120 is less than the width of theconductive layer 113, as shown in FIG. 3 or FIG. 4. The presentinventive concept, however, is not limited thereto. For example, thewidth W1 of the back side contact 120 may be substantially the same asthe width of the conductive layer 113 or greater than the width of theconductive layer 113. The back side contact 120 needs to be formed notto be in contact with the substrate 101 or the photodiode PD. In otherwords, at least one portion of the back side contact 120 may escape theconductive layer 113 but should not escape the sidewall insulating layer111. For example, the lower portion of the back side contact 120 needsto be surrounded by the sidewall insulating layer 111.

The back side contact 120 may be disposed in the grid point portion ofthe pixel separation structure 110. For example, the grid portion of thepixel separation structure 110 receives the back side contact 120. Thepresent inventive concept, however, is not limited thereto. For example,the back side contact 120 need not be located at each of the grid pointportion in plural of the pixel separation structure 110. The back sidecontact 120 may be disposed only at some of the grid point portion inplural. In this case, a number of the back side contact 120 in plural issmaller than a number of the grid point portion in plural.

Further, if the side portions of the pixel separation structure 110 havea sufficiently great width, the back side contact 120 may be disposed ata side portion of the pixel separation structure 110. In this case, theback side contact 120 may be disposed between sides of two pixelsadjacent to each other.

Unlike FIG. 1 in which the back side contact 120 is formed in a gridstructure over the pixel separation structure 110, if a back sidecontact has a grid structure, an incident light may be blocked orreflected by the back side contact so that QE may be significantlylowered. For example, in a case in which light is obliquely incident ona pixel, the back side contact portion disposed on the pixel separationstructure 110 may also contribute to QE. Accordingly, when the back sidecontact 120 is formed only at the grid point portion of the pixelseparation structure 110, as in the image sensor 100 of the presentembodiment, by roughly checking QE with an area of the back side contactwith respect to an area of the APS area, an area ratio of the back sidecontact may be less than several percent. In contrast, if the back sidecontact is formed in a grid structure similar to the pixel separationstructure 110, the area ratio of the back side contact may be equal toor greater than 20%. As a result, QE of the image sensor 100 of thepresent embodiment in which the back side contact 120 is formed only atthe grid point portion may be remarkably high, as compared with theimage sensor in which the back side contact is formed in the gridstructure.

The interlayer insulating layer 130 and the multi-layeredinterconnection 140 are disposed on the front surface FS of thesubstrate 101. The interlayer insulating layer 130 includes multiplelayers—a first insulating layer 131, a second insulating layer 133 and athird insulating layer 135. The number of layers of the interlayerinsulating layer 130 is not limited to three layers. For example, theinterlayer insulating layer 130 may include four or more layers. Themulti-layered interconnection 140 includes a first interconnection layer141 on the first insulating layer 131 and a second interconnection layer143 on the second insulating layer 133. The number of layers of themulti-layered interconnection 140, however, is not limited to twolayers. For example, the multi-layered interconnection 140 may includethree or more interconnection layers based on the number of layers ofthe interlayer insulating layer 130. The multi-layered interconnection140 may further include the interconnection layer 141 a.

The first interconnection layer 141, the second interconnection layer143 and the interconnection layer 141 a of the multi-layeredinterconnection 140 may be electrically connected to each other throughvertical contacts 142 and 142 a and may be electrically connected toactive areas of the substrate 101 and the conductive layer 113 of thesubstrate 101. The multi-layered interconnection 140 may extend to aperipheral circuit area outside the APS area. Meanwhile, referencenumeral ‘a’ may be attached to the interconnection layer 141 a and thevertical contact 142 a connected to the conductive layer 113 of thepixel separation structure 110 to distinguish the first interconnectionlayer 141 and the vertical contact 142.

The antireflection layer 151, the color filter 162, and the micro-lens164 are disposed on the back side BS of the substrate 101. Theantireflection layer 151 may prevent reflection of light incident on theback side BS of the substrate 101 and may be formed of, for example,hafnium oxide (HfOx). However, the material of the antireflection layer152 is not limited thereto. The color filter 162 may be arranged in anarray structure corresponding to the pixel P. In an exemplaryembodiment, the color filter 162 may have a Bayer pattern structureincluding a red filter, a green filter, or a blue filter. In anexemplary embodiment, the color filter 162 may include a yellow filter,a magenta filter, or a cyan filter. In addition, the color filter 162may further include a white filter.

A peripheral circuit area (not shown) may be disposed outside the APSarea. A plurality of CMOS circuits for signal processing of an image maybe disposed in the peripheral circuit area. A voltage application devicemay be disposed in the peripheral circuit area. The voltage applicationdevice may apply a negative voltage or a ground voltage suitable forcharge removal to the conductive layer 113 of the pixel separationstructure 110 through the interconnection layer 141 a. In addition, theapplied ground voltage or negative voltage may be applied to the backside contact 120 through the conductive layer 113. Accordingly, chargesaccumulated or remaining on the interface between the back side BS ofthe substrate 101 and the antireflection layer 151 may be dischargedthrough the back side contact 120, the conductive layer 113, and thefirst interconnection layer 141 a, and thus the ESD bruise defectproblem caused by accumulation of charges on the interface may beeffectively removed.

FIGS. 5A through 5C are plan views of image sensors 100 a, 100 b, and100 c according to an exemplary embodiment. The image sensors 100 a. 100b and 100 c are substantially the same as the image sensor 100 of FIGS.1 to 4, except the shape of the back side contact 120. The plan views ofFIGS. 5A through 5C correspond to FIG. 4.

Referring to FIG. 5A, the image sensor 100 a may have a back sidecontact 120 a different from the image sensor 100 of FIG. 4. Forexample, the back side contact 120 a has an elliptical shape with itslong axis in a first direction (x direction). The image sensor 100 a hasa pixel separation structure 110 a different from the image sensor 100of FIG. 4. The first pixel separation structure 110 a a first sideportion 113 a-1 extending in a second direction (y direction) and asecond side portion 113 a-2 extending in the first direction (xdirection). The first side portion 113 a-1 has a first side width Dx,and the second side portion 113 a-2 has a second side width Dy. Thefirst side width Dx is greater than the second side width Dy. Also, awidth in the first direction (x direction) may be greater than a widthin the second direction (y direction) in a grid point portion of thepixel separation structure 110 a. In this case, the back side contact120 a has an elongated ellipse in the first direction (x direction). Thepresent inventive concept is not limited thereto, a back side contactmay be formed in a circular shape as in the image sensor 100 of FIG. 4.

Referring to FIG. 5B, the image sensor 100 b has a back side contact 120b different from the image sensor 100 of FIG. 4. For example, the backside contact 120 b has a rectangular shape. In addition, the back sidecontact 120 b is positioned such that vertexes of the rectangle aredirected in parallel to the sides of the pixel separation structure 110.The shape of the back side contact 120 b is not limited to a square. Forexample, the back side contact 120 b may have various polygonal shapessuch as triangular, pentagonal, and hexagonal.

Referring to FIG. 5C, the image sensor 100 c has a back side contact 120c different from the image sensor 100 of FIG. 4. For example, the backside contact 120 c has a cross shape. In addition, the back side contact120 c is arranged such that cross-shaped protruding portions aredirected in parallel to side portions of the pixel separation structure110. The cross shape of the back side contact 120 c is wider at acentral portion than an end portion.

The present inventive concept is not limited thereto. For example, aback side contact disposed at a grid point portion of a pixel separationstructure and connected to a conductive layer may have various shapes.In addition, in FIGS. 5A to 5C, only a shape of an upper surface of theback side contact is described, but a three-dimensional shape of theback side contact may basically have a column shape. Accordingly, thethree-dimensional shape of the back side contact will be described withreference to FIGS. 6A to 6C.

FIGS. 6A through 6C are perspective views of 3D structures of the backside contact 120 formed in the image sensor 100 of FIG. 1.

Referring to FIG. 6A, the image sensor 100 includes the back sidecontact 120 having a three-dimensional cylindrical shape. Thethree-dimensional shape of the back side contact 120 is not limited to acylinder. For example, the back side contacts 120 a, 120 b, 120 cillustrated previously in FIGS. 5A through 5C may also have columnarshapes. In other words, the back side contact 120 a of FIG. 5a has anelliptical column shape, the back side contact 120 b of FIG. 5B has aquadrangular column shape, and the back side contact 120 c of FIG. 5Cmay have a cross column shape. If a top surface of the back side contacthas a polygonal shape such as a triangle and a pentagon, thethree-dimensional shape of the back side contact may have a polygonalcolumn shape such as a triangular cylinder and a pentagonal cylinder.

Referring to FIG. 6B, an image sensor 100 d includes a back side contact120 d having a circular truncated cone shape three dimensionally. Inother words, the back side contact 120 d has a shape in which an areabecomes narrower toward the bottom. If an upper surface of the back sidecontact 120 d is an ellipse, the back side contact has a shape of anelliptical truncated cone. If the upper surface of the back side contact120 d has a polygonal shape such as a triangle, a rectangle and apentagon, the back side contact 120 d may have a shape of a polygonaltruncated cone, such as a triangular truncated cone, a quadrangulartruncated cone, and a pentagonal truncated cone.

Referring to FIG. 6C, the image sensor 100 e includes a back sidecontact 120 e having an upper head portion 122 having a large area and alower insertion portion 124 having a small area. The upper head portion122 may be a portion located on an upper surface of the conductive layer113 of the pixel separation structure 110. The lower insertion portion124 may be a portion inserted into the conductive layer 113. This backside contact 120 e may have a shape similar to a tack. A verticalcross-section of the back side contact 120 e has a ‘T’ shape. The upperhead portion 122 is not limited to a cylinder, but may have a shape suchas an elliptical column, a polygonal column, and a cross column, asdescribed with reference to FIG. 6A. Further, as described withreference to FIG. 6B, the upper head portion 122 may have a shape suchas a truncated cone, an elliptical truncated cone, and a polygonaltruncated cone. Furthermore, the shape of the insertion portion 124 isnot limited to the cylinder.

In an exemplary embodiment, a seam may be present in a central portionof the conductive layer 113 of the pixel separation structure 110 andthe insertion portion 124 of the back side contact 120 e may be easilyinserted in the conductive layer 113.

FIGS. 7, 8A and 8B, and 9A through 9E are cross-sectional views of animage sensor 100 e, an image sensor 100 f, an image sensor 100 g, animage sensor 100 h, an image sensor 100 i, an image sensor 100 j, animage sensor 100 k, and an image sensor 100 l according to an exemplaryembodiment. FIGS. 7, 8A and 8B, and 9A through 9E correspond to FIG. 3.

Referring to FIG. 7, the image sensor 100 e includes a back side contact120 e different from the image sensor 100 of FIG. 3. For example, theback side contact 120 e has the tack shape of FIG. 6C. The back sidecontact 120 includes the upper head portion 122 and the lower insertionportion 124. The upper head portion 122 is located on an upper surfaceof the conductive layer 113 of the pixel separation structure 110, andthe inserting portion 124 is inserted into the conductive layer 113.

The upper head portion 122 has a first width W1′ that may be greaterthan the first width W1 of the back side contact 120 of FIG. 3. A secondwidth W2′ between the sidewall insulating layer 111 and the upper headportion 122 may be smaller than the second width W2, which is aseparation distance of the back side contact 120 of FIG. 3 from thesidewall insulating layer 111.

Referring to FIG. 8A, the image sensor 100 f further includes a backside insulating layer 153 on the back side BS of the substrate 101compared with the image sensor 100 of FIG. 3. For example, the back sideinsulating layer 153 is disposed on the antireflection layer 151. Theback side insulating layer 153 may serve as an insulating layer forplanarization, for example. After forming the antireflection layer 151,the back side insulating layer 153 may be formed by applying atransparent insulating material on the entire surface of theantireflection layer 151 and performing a planarization process such asa chemical mechanical polishing (CMP) process thereon. The back sideinsulating layer 153 may be formed to form the color filter 162 and themicro-lens 164 on the upper surface of the back side insulating layer153 at a uniform height from the back side BS of the substrate 101.

Although not shown, a passivation layer may further be formed on theupper surface of the back side insulating layer 153 for protecting theback side insulating layer 153 and components below the back sideinsulating layer 153.

Referring to FIG. 8B, the image sensor 100 g includes a back sidecontact 120 f different from the image sensor 100 f of FIG. 8A. Forexample, the back side insulating layer 153 is formed on theantireflection layer 151 and the back side contact 120 f penetrates theantireflection layer 151 and the back side insulating layer 153. A lowerportion of the back side contact 120 f is inserted into the conductivelayer 113 of the pixel separation structure 110.

In an exemplary embodiment, the back side contact 120 f need notcompletely penetrate the back side insulating layer 153 so that the backside contact 120 f may penetrate partially the back side insulatinglayer 153. For example, an upper portion of the back side contact 120 fmay protrude from the antireflection layer 151, and a side surface andan upper surface of the protruded upper portion may be covered with theback side insulating layer 153.

Referring to FIG. 9A, the image sensor 100 h includes a pixel separationstructure 110 b different from the image sensor 100 of FIG. 3. Forexample, the pixel separation structure 110 b need not penetrate the STIlayer 103 a. The pixel separation structure 110 b is in contact with anupper surface of the STI layer 103 a. In addition, as the pixelseparation structure 110 b is coupled to the STI layer 103 a on theupper surface of the STI layer 103 a, a vertical contact 142 a′penetrates the first insulating layer 131 and the STI layer 103 a toconnect a first interconnection layer 141 a′ and the conductive layer113 b of the pixel separation structure 110 b may have a structure thatthe vertical contact 142 a′. Thus, a length of the vertical contact 142a′ of the image sensor 100 h may be greater than the vertical contact142 a of the image sensor 100 of FIG. 3.

The hack side contact 120 is connected to the conductive layer 113 h ofthe pixel separation structure 110 b through the antireflection layer151 at the back side BS of the substrate 101. Further, the pixelseparation structure 110 b may be arranged in a two-dimensional gridstructure on an x-y plane (for example, in a planar view of the imagesensor 100 h), and the back side contact 120 may be arranged in a gridpoint portion of the pixel separation structure 110 b

The image sensor 100 of FIG. 3 may be fabricated by firstly forming theSTI layer 103 a on the substrate 101 and then forming the pixelseparation structure 110 on the STI layer 103 a. On the other hand, theimage sensor 100 h of FIG. 9A may be fabricated by firstly forming thepixel separation structure 110 b on the substrate 101, and then formingthe STI layer 103 a on the pixel separation structure 110 b. Meanwhile,the image sensor 100 of FIG. 3 and the image sensor 100 h of FIG. 9A maybe fabricated by forming deep trenches in the front side FS of thesubstrate 101 and filling the deep trenches with the sidewall insulatinglayers 111 and 111 h and the conductive layers 113 and 113 b to form thepixel separation structures 110 and 110 b.

Referring to FIG. 9B, the image sensor 100 i is different from the imagesensor 100 of FIG. 3. For example, the pixel separation structure 110 isnot coupled to the STI layer 103 a of FIG. 3. The STI layer 103 a ofFIG. 3 is absent in the image sensor 100 i of FIG. 9B. The pixelseparation structure 110 may be also formed by forming a deep trench inthe front side FS of the substrate 101 and filling the deep trench withthe sidewall insulating layers 111 and 111 b and the conductive layers113 and 113 b.

The back side contact 120 is connected to the conductive layer 113 ofthe pixel separation structure 110 through the antireflection layer 151at the back side BS of the substrate 101. In addition, the back sidecontact 120 may be disposed at a grid point portion of the pixelseparation structure 110.

Referring to FIG. 9C, the image sensor 100 j includes a pixel separationstructure 110 c, a first interconnection layer 141 b and a verticalcontact 142 b different from the image sensor 100 of FIG. 3. Forexample, the pixel separation structure 110 c is combined with the STIlayer 103 a. For example, the pixel separation structure 110 c is incontact with the STI layer 103 a. The pixel separation structure 110 cincludes a sidewall insulation layer 111 c a conductive layer 113 c. Thesidewall insulation layer 111 c covers a side surface and a bottomsurface of the conductive layer 113 c. For example, the sidewallinsulation layer 111 c is in contact with the side surface of theconductive layer 113 c and the bottom surface of the conductive layer113 c. The sidewall insulation layer 111 c of the pixel separationstructure 110 c is exposed on the front side FS of the substrate 101instead of the conductive layer 113 c.

The image sensor 100 j further includes the first interconnection layer141 b and the vertical contact 142 b for applying a negative voltage ora ground voltage to the conductive layer 113 c of the pixel separationstructure 110 c. The first interconnection layer 141 b and the verticalcontact 142 b are formed on the back side BS of the substrate 101. Thefirst interconnection layer 141 b and the vertical contact 142 b may bedisposed at an outer portion of the APS area to avoid an interfere witha path of light incident on the back side BS. The image sensor 110 jfurther includes a back side insulating layer 153 disposed between theantireflection layer 151 and the color filter 162. The back sideinsulating layer 153 may be, for example, an insulating layer forplanarization.

The image sensor 100 j may be fabricated by forming a deep trenchextending from the back side BS to the front side FS of the substrate101 and filling the deep trench with the sidewall insulating layer 111 cand the conductive layer 113 c to form the pixel separation structure110 c. For example, the STI layers 103 a and 103 b may be firstly formedon the front side FS of the substrate 101, and the multi-layeredinterconnection 140 may be formed on the front side FS of the substrate101. Next, a deep trench may be formed in the back side BS of thesubstrate 101 and may be filled with the sidewall insulating layer 111 cand the conductive layer 113 c to form the pixel separation structure110 c. Next, the antireflection layer 151 may be formed on the substrate101, and the back side contact 120, the vertical contact 142 b, and thefirst interconnection layer 141 b may be formed. Finally, the imagesensor 100 j of the present embodiment may be fabricated by forming theback side insulating layer 153, the color filter 162, and the micro-lens164.

Referring to FIG. 9D, the image sensor 100 k includes a pixel separationstructure 110 d different from the image sensor 100 j of FIG. 9C. Forexample, the pixel separation structure 111 d is in contact with anupper surface of the STI layer 103 a without passing through the STIlayer 103 a. In addition, the pixel separation structure 110 d (includesa sidewall insulating layer 111 d and a lower surface of the conductivelayer 113 d. The sidewall insulating layer 111 d covers the lowersurface of the conductive layer 113 d. For example, the sidewallinsulating layer 111 d is in contact with the lower surface of theconductive layer 113 d. In other words, the sidewall insulating layer111 d may extend from a side surface of the conductive layer 113 d andcover a bottom surface of the conductive layer 113 d.

The image sensor 100 k may be fabricated by forming a deep trench in theback side BS of the substrate and filling the deep trench with thesidewall insulating layer 111 d and the conductive layer 113 d to formthe pixel separation structure 110 d. However, unlike the image sensor100 j of FIG. 9C, the deep trench need not penetrate the STI layer 103 abut may be formed only up to a top surface of the STI layer 103 a, andthereafter, the sidewall insulating layer 111 d and the conductive layer113 d may be filled in the deep trench, thereby forming the pixelseparation structure 110 d.

Referring to FIG. 9E, the image sensor 100 l is different from the imagesensor 100 j of FIG. 9C. For example, the pixel separation structure 110c of FIG. 9E need not be coupled with the STI layer 103 a of FIG. 9C. Inother words, the STI layer 103 a of FIG. 9C is not present in the imagesensor 100 j. The pixel separating structure 110 c may be formed byforming a deep trench extending from the back side BS of the substrate101 to the front side FS of the substrate 101 and filling the deeptrench with the sidewall insulating layer 111 c and the conductive layer113 c.

The present inventive concept is not limited to the exemplary embodimentdescribed above. For example, in an image sensor in which a pixelseparation structure of a grid structure is formed, the image sensor mayinclude a back side contact with various structures that is in contactwith a conductive layer of the pixel separation structure at a back sideof a substrate. The back side contact may be arranged at a grid pointportion of the pixel separation structure at the back side.

FIG. 10 is a schematic block diagram of a camera system 200 including animage sensor according to an exemplary embodiment.

Referring to FIG. 10, the camera system 200 includes an image sensingunit 210, an image signal processing unit 220, and an image display unit230. The image sensing unit 210 includes a control resister block 211, atiming generator 212, a ramp signal generator 213, a buffer unit 214, anactive pixel sensor (APS) array 215, a row driver 216, a correlateddouble sampler 217, a comparator 218, and an analog to digital converter(ADC) 219.

The control resister block 211 may control all operations of the camerasystem 200. The control resister block 211 may directly provide anoperation signal to the timing generator 212, the ramp signal generator213, and the buffer unit 214. The timing generator 212 may generate asignal used as a reference signal for an operation timing of componentsof the image sensing unit 210. The operation timing reference signalgenerated by the timing generator 212 may be applied to the row driver216, the correlated double sampler 217, the comparator 218, or the ADC219. The ramp signal generator 213 may generate a ramp signal used bythe correlated double sampler 217 or the comparator 218 and apply theramp signal to the correlated double sampler 217 or the comparator 218.The buffer unit 214 may include a latch unit. The buffer unit 214 maytemporarily store an image signal to be transmitted to the outside ofthe buffer unit 214.

The APS array 215 may sense an external image. The APS array 215 mayinclude a plurality of active pixels, and the APS areas of the imagesensors 100, 100 a˜100 l may be part of the APS array 215. The rowdriver 216 may selectively activate a row of the APS array 215. Thecorrelated double sampler 217 may sample an analog signal generated bythe APS array 215 and output the sampled analog signal. The comparator218 may compare data provided from the correlated double sampler 217with a slope of the ramp signal feedback in accordance with analogreference voltages to generate a variety of reference signals. The ADC219 may convert analog image data to digital image data.

While the present inventive concept has been shown and described withreference to exemplary embodiments thereof, it will be apparent to thoseof ordinary skill in the art that various changes in form and detail maybe made therein without departing from the spirit and scope of theinventive concept as defined by the following claims.

What is claimed is:
 1. An image sensor comprising: a substratecomprising a plurality of pixels arranged in a two-dimensional arraystructure, and having a front side and a back side opposite to the frontside; an interconnection arranged on the front side of the substrate; aninsulating layer arranged on the back side of the substrate; a pixelseparation structure disposed in the substrate, wherein the pixelseparation structure separates the plurality of pixels from each otherand includes a conductive layer therein; and a contact disposed on theback side of the substrate and electrically connected the conductivelayer of the pixel separation structure.
 2. The image sensor of claim 1,wherein the pixel separation structure has a grid structure in a planarview of the image sensor and surrounds each of the plurality of pixels.3. The image sensor of claim 1, wherein the conductive layer penetratesthe substrate to be electrically connected to the interconnection. 4.The image sensor of claim 1, wherein a negative voltage or a groundvoltage is applied to the conductive layer and the contact through theinterconnection.
 5. The image sensor of claim 1, wherein a part of thecontact is inserted into the conductive layer.
 6. The image sensor ofclaim 1, wherein an upper surface of the contact has one of a circularshape, an elliptical shape, a polygonal shape, and a cross shape.
 7. Theimage sensor of claim 1, wherein the plurality of pixels includes fourpixels arranged in two rows and two columns, and wherein the contact iscentered and spaced apart from the four pixels.
 8. The image sensor ofclaim 1, wherein the pixel separation structure has a grid structure ina planar view of the image sensor, and wherein the contact is disposedin some of grid points of the grid structure.
 9. The image sensor ofclaim 1, wherein each of the plurality of pixels includes a photodiode,and wherein the photodiode is surrounded by a sidewall insulating layerso that the photodiode is isolated from the conductive layer of thepixel separation structure.
 10. The image sensor of claim 1, wherein theconductive layer includes polysilicon, and wherein the contact includestungsten (W).
 11. An image sensor comprising: a plurality of pixels eachcomprising a photodiode and disposed in an array structure on asubstrate, the substrate comprising a front side and a back sideopposite to the front side; a pixel separation structure penetrating thesubstrate, wherein the pixel separation structure separates theplurality of pixels from each other and includes a conductive layertherein; and a plurality of contacts disposed on the back side of thesubstrate and electrically connected the conductive layer of the pixelseparation structure.
 12. The image sensor of claim 11, furthercomprising an interconnection on the front side of the substrate,wherein the conductive layer is electrically connected to theinterconnection, and wherein a negative voltage or a ground voltage isapplied to the conductive layer and the plurality of contacts throughthe interconnection.
 13. The image sensor of claim 11, furthercomprising an insulating layer on the back side of the substrate,wherein each of the plurality of contacts penetrates the insulatinglayer to be electrically connected the conductive layer.
 14. The imagesensor of claim 13, wherein the insulating layer includes hafnium oxide(HfOx), wherein the conductive layer includes polysilicon, and whereinthe plurality of back side contacts includes tungsten (W).
 15. The imagesensor of claim 11, wherein the pixel separation structure has a gridstructure in a planar view of the image sensor, and wherein theplurality of contact are disposed in some of grid points of the gridstructure.
 16. An image sensor comprising: a substrate; a plurality ofphotodiodes disposed in an array structure on the substrate; a pixelseparation structure penetrating the substrate, surrounding each of theplurality of photodiodes, separating the plurality of photodiodes fromeach other, and including a conductive layer therein; an interconnectionarranged on the front side of the substrate and electrically connectedto the conductive layer of the pixel separation structure; an insulatinglayer arranged on the back side of the substrate; and a plurality ofcontacts disposed on the back side of the substrate, penetrating theinsulating layer, and electrically connected to the conductive layer ofthe pixel separation structure.
 17. The image sensor of claim 16,further comprising a voltage source, wherein the plurality of contactselectrically connected to the interconnection through the pixelseparation structure, and wherein a negative voltage or a ground voltagefrom the voltage source is applied to the conductive layer and theplurality of contacts through the interconnection.
 18. The image sensorof claim 16, wherein the pixel separation structure further comprises aplurality of sidewall insulating layers each of which is interposedbetween the conductive layer and one of the plurality of photodiodes.19. The image sensor of claim 16, wherein the plurality of contacts arepartially inserted into the pixel separation structure.
 20. The imagesensor of claim 19, wherein the plurality of contacts are partiallyinserted into the conductive layer of the pixel separation structure.